For 13.04:

The migration of Pidgin to the new libmessaging-menu API, which caused this issue, is now done for Pidgin, but still under testing. Also, only a Ubuntu 13.04 package is provided so far, but since it does not introduce any dependencies on other stuff from 13.04, I was able to just install it from the PPA of the programmer who fixed it. According to his instructions, this is what fixed it for me:

In 11.10 Unity has hidden the system tray access to pidgin under the messaging icon that looks like an envelope. If you click it, there should be an entry for Pidgin. Not exactly what you're looking for, but at least it's accessible somehow via the system tray.